Helicopters often include a tail rotor assembly, which includes two or more blades rotated about a central axis of rotation to generate thrust. The thrust can be used to counter the torque effect created by a main rotor assembly and can also be used to allow a pilot to control the yaw of a helicopter. The amount and direction of the thrust is generally controlled by collectively changing the angles of attack of all of the tail rotor blades together.
Tail rotor blades can also accommodate at least some amount of cyclic flapping and feathering to counter the dissymmetry of lift phenomenon that occurs as a helicopter moves through the air. For example, as a tail rotor blade moves in the same direction as the helicopter movement (e.g., an advancing blade in forward flight), the tail rotor blade experiences a greater air speed, generates more thrust, and flaps in the direction opposite to the thrust. In another example, as a tail rotor blade moves in the opposite direction as the helicopter movement (e.g., a retreating blade in forward flight), the tail rotor blade experiences a lower air speed, generates less thrust, and flaps in the direction of the thrust. To compensate for the dissymmetry of lift and control the amount of flapping, tail rotor blades can be designed to decrease the angle of attack of the blades as the blades move in the same direction as the helicopter movement and increase the angle of attack of the blades as they move in the opposite direction of the helicopter movement. The cyclic changing of the angles of attack is commonly referred to as feathering or delta-3 and is used to balance the thrust generated by each of the tail rotor blades and limit flapping angles.